Interpretive Summary: The wheat stem sawfly, Cephus cinctus, is a major pest limiting the production of wheat in the northern Great Plains of North America. Understanding the chemical ecology of C. cinctus could lead to new and environmentally friendly approaches for reducing agricultural damage, especially since insecticides are ineffective against this insect. In this research, we were able to demonstrate that male and female insects communicate with each other using unique blends of compounds (pheromone) that are derived primarily through an oxidation process of compounds naturally present on the bodies of the insects. Evidence that C. cinctus releases and detects this pheromone blend was obtained by utilizing the antennal "nose" of the insects. Electrophysiological recording made from the antennae of the insects allowed us to pinpoint and identify those compounds that are emitted by the insects to attract others of the same species. A synthetic version of one of the chemicals present in the pheromone blend was tested in a wheat field, and the data demonstrated that C. cinctus is attracted to this single compound. This study has defined those chemicals that are important in the chemical communication of C. cinctus, and this information may contribute towards an environmentally friendly control of this agricultural pest.

Technical Abstract:
Volatile collections and cuticular extracts of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), were analyzed by coupled gas chromatographic-electroantennographic detection (GC-EAD) in order to elucidate the pheromone of this species. Volatile collections of male and female sawflies revealed the same 13 GC-EAD-active compounds that stimulate both male and female antennae. GC-EAD-active compounds were identified using coupled gas chromatographic-mass spectrometric (GC-MS) analysis and GC and MS comparison to authentic standards. The most antennally-active compound was 9-acetyloxynonanal. Additional GC-EAD-active compounds were identified as 13- acetyloxytridecanal, aldehydes with 9 to 16 carbon chain lengths, acids with 8 to 10 carbon chain lengths, and phenylacetic acid. The last was instantly detectable by human nose when several males were allowed to interact, but not from isolated insects. On a per-insect basis, grouped males released overall higher amounts of the GC-EAD-active compounds than single insects or grouped females. Notable quantitative differences between the sexes were relatively higher amounts of 9-acetyloxynonanal, phenylacetic acid and tetradecanal from males and hexadecanal from females. In the absence of an absolute, qualitative difference between sexes, these relative differences might be important for sex recognition. The major compounds of male and female cuticular extracts showed no GC-EAD activity, but ozonolysis of extracts gave dramatically increased amounts of